1. Field of the Invention
In some aspects, the present invention relates to apparatus and methods for separation of liquids of different densities in production fluid streams from underground wells. More specifically, these aspects of the invention relate to the separation of water and oil in production fluids. The present invention also relates to apparatus and methods for pumping and transport of the separated liquids to the surface or to other portions of a wellbore. In other aspects, the invention also relates to methods and apparatus for reinjection of separated water from production fluid into formations to stimulate flow of hydrocarbons. Other aspects of the disclosed invention include new separation arrangements which incorporate gas or liquid driven motors, designs for multi-stage hydrocyclone separators, and use of beam or rod pumps.
2. Description of Related Art
Recently, the value has been recognized of employing a downhole separator apparatus such as a hydrocyclone-based separator in producing oil wells. A hydrocyclone-based separator is capable of substantially separating a mix of two liquids of different densities into two streams of those constituent liquids. The separator apparatus is designed to receive a production stream of oil which contains a significant amount of water, the production stream being obtained from production perforations leading to a producing zone within the surrounding formation. The separator then receives the production stream and substantially separates the oil from the water to produce a clean water stream which has a low concentration of oil and a concentrated oil stream from which the water has been substantially removed. Typically, the clean water stream is then directed toward injection perforations in another potential production zone or another area of the current production zone. This area is referred to as the disposal or injection zone. A suitable separator assembly for such applications, as well as the applications described herein, is the VORTOIL.RTM. Downhole Oil Water Separator assembly available commercially from Baker-Hughes Process Systems, 6650 Roxburgh, Suite 180, Houston, Tex. 77041. Aspects of the construction and operation of some separator assemblies are also described in U.S. Pat. Nos. 5,296,153, "Method and Apparatus for Reducing the Amount of Formation Water in Oil Recovered from an Oil Well," and 5,456,837, "Multiple Cyclone Apparatus and Downhole Cyclone Oil/Water Separation," both issued to Peachey; International PCT Published Patent Application WO 94/13930, entitled "Method for Cyclone Separation of Oil and Water and Means for Separating of Oil and Water," as well as other patents and publications.
The separator assembly is normally coupled with a fluid pump such as a multi-stage centrifugal pump or a progressive cavity pump (PCP) as well as a motor which drives the pump to assist in bringing the concentrated oil stream to the surface. Collectively, these arrangements are referred to as motor-pump-separator assemblies.
If the clean water stream is directed to injection perforations located below or downhole from the production perforations, this is known as a downhole arrangement. Conversely, if the injection perforations are located above or uphole from the production perforations, this is known as an uphole arrangement.
Typically, the drilling arrangements which use motor, pump and separator assemblies of this type have well casing diameters measuring 5-1/2 inches, 7 inches or 9-5/8 inches. However, these are merely standard conventional measurements and are not intended to limit this discussion or application of the present invention. Packers made for systems of this size are useful for packing off tubing which has a relatively small outer diameter as compared to the inner diameter of the production casing. In a 5-1/2 inch casing, for example, the packer would be capable of packing off a tubing or other member which is roughly 3 inches in diameter or smaller. However, it would be difficult if not impossible without the use of specialized equipment to pack off tubular members having a diameter larger than 3 inches within such a casing.
Other problems exist with arrangements which require more than one pump to assist in transmitting the concentrated oil stream toward the surface of the well. Certain arrangements require dual pumps to assist transmission of the concentrated oil stream toward the surface of the well. In current practice using a dual pump arrangement, a motor is centrally located and attached by means of seal above and below to two pumps. The first pump is a high volume, low head pump which moves the concentrated oil stream upward to the second pump which is a low volume, high head pump and which functions primarily to assist the concentrated oil stream toward the surface. The prior art method uses a single motor to drive both pumps. The prior art method may not be suitable in certain situations such as where the secondary pump must be placed too deeply to be effective in assisting the oil to the surface.
It is an object of the present invention to provide for motor, pump and separator assemblies which are capable of improved operation over prior art systems.